The objectives of the proposed research are to study the organization of a sensory pathway in detail and to determine the effects of sensory deprivation upon the structure of the pathway. The visual pathway has been chosen for special study. The laminar distribution of neuronal and synaptic types within the geniculate relay will be studied by light (Golgi and Nissl) and electron microscopical methods in order to demonstrate the significance of the lamination, to reveal possibilities of interlaminar interactions, and to provide a base line for deprivation studies. Cat, Macaque and Tree Shrew, which show different patterns of lamination and different patterns of binocular interaction will be used. The organization of the receptive layer of the visual cortex (layer IV) will be studied in the tree shrew by Golgi and electron microscopical methods, and this will be related to knowledge of geniculate organization in this species. Changes that occur in the lateral geniculate nucleus, the visual cortex and corticofugal fiber systems as a result of visual deprivation will be studied by light and electron microscopical methods, by fiber degeneration methods and by autoradiographic methods in several different species.